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BioMed Research International
Volume 2015, Article ID 131623, 12 pages
Research Article

Listeriosis Outbreaks in British Columbia, Canada, Caused by Soft Ripened Cheese Contaminated from Environmental Sources

1Environmental Health Services, BC Centre for Disease Control, 655 West 12th Avenue, Vancouver, BC, Canada V5Z 4R4
2Immunization Programs and Vaccine Preventable Diseases Services, BC Centre for Disease Control, 655 West 12th Avenue, Vancouver, BC, Canada V5Z 4R4
3School of Population and Public Health, University of British Columbia, Vancouver, BC, Canada V6T 1Z9

Received 22 August 2014; Revised 19 December 2014; Accepted 22 December 2014

Academic Editor: Petr Kralik

Copyright © 2015 Lorraine McIntyre et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Soft ripened cheese (SRC) caused over 130 foodborne illnesses in British Columbia (BC), Canada, during two separate listeriosis outbreaks. Multiple agencies investigated the events that lead to cheese contamination with Listeria monocytogenes (L.m.), an environmentally ubiquitous foodborne pathogen. In both outbreaks pasteurized milk and the pasteurization process were ruled out as sources of contamination. In outbreak A, environmental transmission of L.m. likely occurred from farm animals to personnel to culture solutions used during cheese production. In outbreak B, birds were identified as likely contaminating the dairy plant’s water supply and cheese during the curd-washing step. Issues noted during outbreak A included the risks of operating a dairy plant in a farm environment, potential for transfer of L.m. from the farm environment to the plant via shared toilet facilities, failure to clean and sanitize culture spray bottles, and cross-contamination during cheese aging. L.m. contamination in outbreak B was traced to wild swallows defecating in the plant’s open cistern water reservoir and a multibarrier failure in the water disinfection system. These outbreaks led to enhanced inspection and surveillance of cheese plants, test and release programs for all SRC manufactured in BC, improvements in plant design and prevention programs, and reduced listeriosis incidence.